1. Field of the Invention
The present invention relates to an inkjet recording apparatus and a method for controlling the same, and more particularly relates to a technology of ejecting inks of a plurality of colors for image formation.
2. Description of the Related Art
In a conventional inkjet recording apparatus, nozzles of respective color heads are configured to be arrayed on the same line in a main scanning direction so that arrangement positions of ink dots of the respective colors can be shared.
When such nozzle arrangement is applied to an inkjet recording apparatus using UV curing inks (ultraviolet curable inks), ink dots of all the colors are arrayed on the same line by one main scanning action. As a result, these ink dots may cause landing interference in the main scanning direction, and undesirably form line-like surface shapes having large depressions and projections. Slight shape difference due to these depressions and projections makes uneven glossiness notable.
To solve this problem, a method has been disclosed in Japanese Patent Application Laid-Open No. 2005-262570 in which difference between depressions and projections in an image is reduced by shifting the center position of dots from an ink with low recording density from the center position of dots from an ink with high recording density. Furthermore, a technology for arranging nozzle positions of respective color heads so as to be shifted from each other in a sub-scanning direction has been disclosed in International Publication No. WO 1997/037854.
However, in the method of Japanese Patent Application Laid-Open No. 2005-262570, since the inks with high recording density are deposited on the same identical line, uneven glossiness is not sufficiently improved in an image with high density and high droplet deposition rate (such as a gray-color solid image made up of four colors of cyan, magenta, yellow, and black). Moreover, if the nozzle arrangement disclosed in International Publication No. WO 1997/037854 is applied to an inkjet recording apparatus using UV curing inks, uneven glossiness is still notable depending on a superimposing order of colors since the UV curing inks are different in cure sensitivity between respective colors due to absorption wavelengths of pigments.
Further, a technology to improve image quality is described in Japanese Patent Application Laid-Open No. 2007-118409, in which inkjet heads of the respective colors are placed at different positions, and an ink with the lowermost penetration is first printed and cured before other inks are printed in sequence.
Placing each color head as described in Japanese Patent Application Laid-Open No. 2007-118409 causes upsizing of carriages that carry the heads as well as an UV irradiation light source, which in turns causes deterioration in scan speed and increase in power consumption.